Mounting of filaments in vacuum tubes



1949. CH. FOULKES I MOUNTING OF FI LAMENTS IN VACUUM TUBES Filed March 26, 1945 In venlur s u L U Q v m E R E H m w N C Patented Feb. 22 1949 MOUNTING F FILAMENTS IN VACUUM TUBES Christopher Henry Foulkes, London, England, assigner to Standard Telephones and Cables Limited, London, England, a British company Application March 26, 1945, Serial No. 584,753 In Great Britain June 6, 1944 Claims.

The present invention relates to improved helical filaments for electric vacuum tubes or like devices and to a method of mounting them.

It has been found that helical filaments commonly used in electric vacuum tubes sometimes become distorted when heated, and this has been traced to the fact that the usual methods of mounting such filaments often cause them to be mechanically strained.

' The principal object of the present invention therefore, is to overcome this difficulty by an improvement in the mounting arrangements.

The invention accordingly provides a helical filament for an electric vacuum or gas-filled tube or lamp, having a point at one end of the helix attached to a fixed conducting support and a point at the other end of the helix fixed to a metal conductor passing coaxially through the helix into a corresponding socket in a second fixed conducting support, the said conductor being secured inside the said socket in such a position mechanical strain.

Accordin to the method of mounting the '"filament also covered by the invention, the conductor is at first arranged to be held loosely in the socket, and is allowed to rotate therein until any strains are removed from the filament before being finally secured to the second support,

The invention also covers a filament for an electric vacuum or gas-filled tube or lamp comprising a multiple helix, the wire or wires of which are each attached'at one end of the helix to a corresponding fixed conducting support, and at the other end of the helix to a cylindrical metal rod passing coaxially through the helix into a metal sleeve fixed to a central conducting support, the said rod being secured to the said metal sleeve in such a position that the wire or wires of the filament are substantially free from mechanical strain.

The invention will be described with reference to the figure of the accompanying drawing which shows a helical filament for a vacuum tube mounted on the stem of the tube according to the invention.

The filament I is shown as a double helix. It is first made to the desired size and shape and is set by heating in an atmosphere of hydrogen. It is then welded or otherwise secured at 2 to the upper end of a conductin rod or wire 3 which forms the filament support, and which passes coaxially through the filament. A socket for the rod 3 is formed by a sleeve or tube 4 of nickel or other suitable metal which surrounds the upper that the helical filament is substantially free from 1 The filament I having been fixed to the rod 3,

the latter is inserted into the sleeve 4 and the lower ends of the filament are attached to corresponding metal rods or wires 1 and 8 also sealed through the stem 6.

The rod or wire 3 is allowed to rotate in the sleeve 3 until it takes up a position such that the filament is substantially free from strain, and it is then firmly secured to the sleeve by spot welding at 9, for example, or in any other suitable way.

The rods 5, l and 8 form the lead-out conductors for the filament I, and may be connected in a suitable manner by wires ID to the terminal pins mounted on the base (not shown) of the vacuum tube in the usual way.

The support for the rod 3 may be arranged in other ways, such as by drilling out a suitable cavity in a metal member corresponding to the rod 5 so as to form a socket in which the rod 3 may easily rotate before it is fixed. It will be evident also, that the filament I may be a single helix, in which case one end is attached to the rod 3 and the other to the rod 1, for example, the rod 8 being omitted. The filament could also comprise a multiple helix havin more than two constituent single helices. In this case there would be a separate rod similar to l or 8 for the lower end of each single helix, and the upper ends of all the single helices would be attached at 2 to the rod 3.

What is claimed is:

l. A helical filament for an electric vacuum tube, a fixed conducting support, a second fixed conducting support having an open ended cylindrical socket, a metal conductor passing coaxially through said helical filament and having One end engaging said cylindrical socket, one

ducting supports, the ends of said filament being rigidly fixed to said conducting supports'an additional fixed conducting support having an openended socket, a metal conductor passing coaxially through 'said helical filament and having one end engaging said cylindrical socket, said filament being rigidly attached to said metal conductor, said metal conductor being secured in said socket in such position that said helical filament is substantially free from localized mechanical strain.

3. A method of mounting a helical filament for an electric vacuum tube which comprises attaching a point at one end of the filament to a conductor which passes coaxially through the filament and is loosely held in a socket in a fixed conducting support, attaching another point of said filament to a corresponding fixed conducting support, allowing the said first conductor to rotate in its socket until the filament has become mechanically unstrained, and then fixing the said first conductor to the first mentioned support.

4. In combination, a helical filament for a vacuumtube, rigid conducting supports rigidly at tached to said filaments at a plurality of portions therealong, one of said conducting supports being fixed in position and rigidly attached to an end portion of said filament, and a second conducting support extending coaxially with said helical filament and being rigidly attached toa second portion on said filament, a third support fixed in position with respect to said first conducting support, said second conducting support being rigidly attached to said third support and fixed in the free unstressed position of said second portion on said filament to make said filament substantially free of any mechanical stress.

5. In combination, a helical filament for a vacuum tube, rigid conducting supports rigidly attaehed to said filaments at a plurality of portions thei:ealong,.one of said conducting'supports being fixed in position and rigidly attached to an end portion Of said filament, and a second conducting support extending coaxially with said helical filament and being rigidly attached to a second portion on said filament, a third support fixed in positionwith respect to said first conductingsupport, said second conducting support being rigidly attached to said third support and fixed in a relative position which substantially compensates for any mechanical stress remaining in said filament after it has been attached to said second conducting support.

CHRISTOPHER HENRY FOULKES.

REFERENCES CI-TED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,6'0'8535 Schwerin' Nov. 30, 1926 1,719,352 Relyea July 9,1929 $107,945 Hull et a1. Feb. 8, 1938 2,111 %6 Bennett Mar. 22, 1938 ammo-so Eitel et a1 May 14, 1946 

